Isolation and Characterizations of a Pentacyclic Glycoside from Methanolic Fraction of Allium sativum (Purple Garlic) Bulbs

Abstract

This study reports the isolation and structural elucidation of a novel pentacyclic glycoside from the methanolic extract of air-dried cloves of Allium sativum (purple garlic), a medicinal plant extensively utilized in traditional medicine for the management of inflammation, gastrointestinal disturbances, respiratory tract infections, asthma, hay fever, and related ailments. The compound, identified as a derivative of a pentacyclic triterpenoid, bears the IUPAC name (2R,3R,4R,5R,6R)-6’-(hydroxymethyl)-1-methyl-(20-(tert-pentyl)-19 -(m-tolyl)-7,8,9,10,11,12,13,14,15, 16, 17, 18, 19,  20, 21, 22-hexadecahydropicenyl) oxy)tetrahydro-2H-pyran-2,3,4-triol. Its isolation was achieved through chromatographic techniques, and its structural features were characterized using a comprehensive suite of spectroscopic methods, including FTIR, ^1H and ^13C NMR, HSQC, and LC-MS. Spectral data revealed characteristic signals for methine, hydroxymethine, glycosidic, aromatic, and aliphatic functional groups, with HSQC establishing clear carbon-proton connectivity. FTIR analysis confirmed the presence of hydroxyl, ether, and aromatic functionalities, while mass spectrometry indicated a molecular ion peak consistent with the molecular formula C₃₂H₅₄O₇ and a molecular weight of 546.5 g/mol. This is the first report of the isolation of this glycosylated oleanane derivative from Allium sativum, further enriching the phytochemical knowledge of the plant and supporting its traditional therapeutic applications.